Oswal Practice Papers CBSE Class 10 Science Solutions (Practice Paper - 7)

Section-A

1. (c) Kidney → Ureter → Urinary bladder → Urethra

Explanation :

Urine from the nephron is transported to the collecting duct, where it enters the ureters. Ureters open from the kidney into the urinary bladder. The urinary bladder holds urine, and as the volume of urine collected increases, so does the size of the bladder. When the CNS sends a voluntary message to the bladder, the bladder muscles contract and the bladder sphincter relaxes, allowing urine to pass through the urethra.

2. (b)

Explanation :

Since, the image formed is inverted for distant objects.

3. (a) ∠A and ∠e

Explanation :

It is clear from the ray diagram that ∠A, ∠e are correctly marked. ∠A represents the angle of the prism which is correctly marked. ∠D represents the angle of deviation which is formed between the emergent ray and incident ray is incorrectly marked. ∠r represents the angle of refraction formed by the refracted ray with the normal is incorrectly marked. ∠i is the angle formed by the incident ray with the normal is incorrectly marked.

4. (b) Cytoplasm

Explanation :

The pyruvate produced during glycolysis usually enters the Kerb’s cycle as acetyl coenzyme A in the mitochondrial matrix, where it provides a reservoir of chemical energy (ATP, NADH and FADH2). Pyruvic acid can be transformed to lactic acid as one of its potential fates in cellular respiration. Under stressful conditions, this often occurs in the cytoplasm of muscle tissue.

5. (b) Factors

Explanation :

Mendel discovered the laws of inheritance. He attributed these traits being encoded by factors. Later studies showed that these factors are genes.

6. (d) R₂ > R₁ > R₃

Explanation :

As it is clear from the graph, the current for the A₂ conductor is less than A₁ and A₁ is less than A₃ we can say I_A₂< I_A₁ < I_A₃.

We know

$$\text{R} =\frac{V}{I}\\\text{or}\space \text{R}\propto\frac{1}{\text{I}}$$

If I is less, then R will be more.

I_A2 < I_A1 < I_A3

R₂ > R₁ > R₃.

7. (c) Alkanes

Explanation :

A homologous series is a family of compounds with the same general formula, same functional group and similar chemical properties. Each family of organic compounds is called a homologous series, for example :

Homologous series of Alkanes with the general formula C_nH_{2n + 2}
Homologous series of Alkene with the general formula C_nH_2n
Homologous series of Alkyne with general formula C_nH_{2n – 2}

Hence, from the general formula of the homologous series of alkanes, this can be confirmed that C₃H₈ belongs to the homologous series of alkanes.

8. (a) Multiple fission is a type of asexual reproduction where a single-parent organism divides into multiple offspring simultaneously.

Explanation :

Multiple fission is a reproductive strategy commonly observed in certain unicellular organisms such as protists and some bacteria. This process involves the parent cell dividing into multiple daughter cells, each of which develops into a new individual organism. The offspring produced through multiple fission are genetically identical to the parent organism. This reproductive strategy allows for rapid population growth and is advantageous in environments with favorable conditions for survival and growth.

9. (c) Divides repeatedly—Divides only once.

Explanation :

Both binary fission and multiple fission are modes of asexual reproduction and occur in the presence of only one parent. In binary fission, the parent cell divides itself into two equal and identical daughter cells. It is the most common form of reproduction in prokaryotes such as bacteria. In multiple fission, a single parent cell is divided into many daughter cells. It is the most common form of reproduction in protists and in some parasitic species.

10. (c) There is no electric current flowing through the circuit.

Explanation :

An ammeter is designed to measure the electric current passing through a circuit. When an ammeter reading is zero, it suggests that there is no electric current flowing through the circuit.

In this scenario, if the ammeter is correctly connected in series with a resistor and the reading is still zero, it indicates that there is no current flowing through the circuit. Possible reasons for this include an open switch, disconnected wires, or a power source that is not providing a voltage difference.

11. (c) The pancreas did not release enough digestive enzymes to digest the fats.

Explanation :

Digestion of fats primarily occurs in the small intestine with the help of pancreatic enzymes, specifically pancreatic lipase. When a person experiences stomach discomfort after consuming a high-fat meal, it suggests that the digestion of fats is not taking place efficiently. In this scenario, if the pancreas does not release enough digestive enzymes, particularly pancreatic lipase, it can lead to the inadequate breakdown of fats. As a result, undigested fats may cause discomfort, such as bloating or stomach pain.

12.

Explanation :

The maximum potential is obtained when cells are connected in series such that the negative terminal of the first cell is connected to the positive terminal of the second cell and so on. E.g.,

13. (d) To favour the precipitation of the soap

Explanation :

A small quantity of common salt is generally added to the reaction mixture of vegetable oil and sodium hydroxide to favour the precipitation of the soap because by adding salt to the suspension mixture, soap is precipitated as a solid. This process is called salting out of soap.

14. (b) Binary fission produces two new organisms.

Explanation :

Only unicellular organisms reproduce through binary fission. In binary fission, a unicellular organism (a cell) divides to form two unicellular organisms (two cells). Binary fission in Amoeba can happen in any plane. Binary fission in Leishmania happens in a definite orientation (plane) to the body because Leishmania has a somewhat organised structure.

15. (c)

Explanation :

The magnetic field lines originate from the magnet’s north pole and curve around to enter the south pole. These lines are closer together near the poles, indicating a stronger magnetic field strength, and spread out as they move away from the magnet.

16. (d) None of these

Explanation :

Characters or traits are the characteristics that a person expresses and can be seen in their phenotype. Height, eye colour, and hair colour are all controlled by genes and can be inherited.

17. (c) A is true but R is false

Explanation :

Magnetic field is not a scalar quantity rather it is a vector quantity which has both magnitude and direction. So, when iron filings are placed around a magnet, they get arranged in a fashion similar to that of magnetic field lines.

18. (a) Both A and R are true and R is the correct explanation of A

Explanation :

The voltmeter is indeed always connected in parallel across the circuit while measuring the potential difference. This is because, in a parallel circuit, the voltage across each component is the same.

The Reason also provided correctly explains why the voltmeter is connected in parallel. By connecting the voltmeter in parallel, we ensure that it measures the same potential difference as the component we are interested in.

19. (a) Both A and R are true, and R is the correct explanation of A.

Explanation :

When lead nitrate is heated, it undergoes decomposition, resulting in the release of brown fumes. The reason to produce these brown fumes is the formation of nitrogen dioxide gas (NO₂) as a byproduct. Nitrogen dioxide is brown in colour, hence explaining the observation of brown fumes.

20. (d) A is False but R is true

Explanation :

Photosynthesis is an endothermic reaction because sunlight energy is absorbed by green plants during this process.

Section-B

Question No. 21 to 26 are very short answer questions.

21. (i) Photochemical decomposition reaction is taking place. The reactions in which a compound breaks down into simple substances in the presence of light are called photochemical decomposition reaction. The colour of salt will change from white to grey.

$$\text{(ii)\space}\text{2 AgCl(s)}\xrightarrow{\text{Sunlight}}\\\text{2Ag(s) + Cl}_2(g)$$

(iii) Silver chloride is used in photography.

(i) Digestion of food is an example of a decomposition reaction because the food we eat mainly contains carbohydrates, proteins and fats. These are decomposed into smaller units such as glucose, amino acids and fatty acids in the presence of enzymes present in the body.

(ii) Rusting of iron is an example of an oxidation reaction. In this process, iron reacts with oxygen and moisture present in the atmosphere and forms a brown layer of iron oxide called rust.

22. No, genetic combinations of the mother do not play a significant role in determining the sex of a new born; because mother has only one type of sex chromosomes i.e., X chromosomes, but a the father has two types of chromosomes X and Y chromosomes. So, all children will inherit the X chromosome from the mother and whether X or Y, bearing sperm from father fertilises the egg will determine the sex of new born.

23.

	Property	Metals	Non-metals
1.	Hardness	Metals are generally hard except sodium and potassium.	Non-metals are soft except diamond.
2.	Malleability and ductility	Metals are malleable and ductile except for zinc.	Non-metals are neither malleable nor ductile. They are brittle in nature.
3.	Conductivity	Metals are good conductors of heat and electricity, except mercury and tungsten.	Non-metals are poor conductors of heat and electricity.
4.	Density	Metals have high density except sodium and potassium.	Non-metals have lower density as compared to metals except for diamond.
5.	Lustre	All the metals have a brilliant shine or lustre.	Non-metals do not have luster except iodine and graphite.

24. (i) The two ways in which biodegradable substances would affect the environment are:

(1) Decomposition of biodegradable substances results in the production of a foul smell.

(2) The area where biodegradable wastes are accumulated serves as a good breeding place for mosquitoes, flies etc. which are the main carriers of germs for diseases like cholera, jaundice, typhoid etc.

(ii) The two ways in which non-biodegradable substances would affect the environment are:

(1) Non-biodegradable substances like pesticides (DDT) enter the food chain and leads to biomagnification.

(2) As non-biodegradable substances cannot be degraded naturally so they accumulate in the soil causing pollution and also reducing the fertility of the soil.

25. (i) A piece of transparent glass bound by two spherical surfaces is called a lens.

(ii) Optical centre of a thin lens is a point on the principal axis of the lens such that a ray of light directed towards it, passes undeviated.

(iii) (a) A convex lens has a real focus.

(b) A concave lens has a virtual focus.

26. In sexual reproduction, male and female gametes from two different individuals unite, leading to variations in offsprings due to the mixing up of genetic material whereas in case of asexual reproduction only single parent is involved and there is no formation of gametes. The ones that are produced sexually have better chances of survival due to mixing up of genetic material between the two different individuals, as there is an increase in genetic variations in the offsprings which provides maximum chances for the survival of species in the changing environment as well as under unfavourable conditions. This variation in species is also essential for evolution.

(i) Budding, fragmentation and regeneration are considered as asexual modes of reproduction because only one parent is involved and no sex cells are involved.

(ii) Regeneration in Planaria.

Section-C

Question No. 27 to 33 are short answer questions.

27. (i) When aluminium is treated with concentrated nitric acid, it becomes inert due to the formation of a thin layer of aluminium oxide on its surface which stops the reaction between aluminium and conc. HNO₃. Thus, conc. HNO₃ can be stored in an aluminium container.

(ii) Aluminium is a highly reactive metal but it is resistant to corrosion. The reason for this is that aluminium reacts with oxygen present in the air to form a thin layer of aluminium oxide. This oxide layer is very stable and prevents further reaction of aluminium with oxygen. It is light in weight and a good conductor of heat. Therefore, it is used to make utensils for cooking.

(iii) 24-carat gold is a pure form of gold and is very soft, so it is not used for making ornaments. Due to this reason, it is alloyed with a small amount of copper or silver to make it hard as required for making ornaments.

28. (i) Carbon can link with carbon atoms via covalent bonds to form long chains, branched chains and closed ring, called catenation. Carbon shows catenation to a large extent because of its small size and having C – C strong bonding.

(ii) A homologous series is a group of organic compounds having similar structures and similar chemical properties in which the successive compounds differ by CH₂ group.
The general formula of the homologous series of alkenes is C_nH_2n where n is the number of carbon atoms in one molecule of alkene.

(iii) The organic compounds having the same molecular formula but different structures are known as isomers. n-butane and iso-butane are two isomers of butane.

29. (i) Decomposers act upon dead and decaying organisms and convert them into simpler forms. These simple substances get mixed up in the soil and are used as nutrients by the producers. From producers, it goes to consumers and so on. They maintain the balance in the ecosystem and provide
space for the new life in the ecosystem.

(ii) Ozone layer is found in the stratosphere which prevents harmful UV rays to reach the earth’s surface. But the depletion of the ozone layer allows more UV rays to pass through it and causes various harmful effects on human beings like cancer, genetic defects, cataract, etc.

(iii) Plants are able to capture only 1% of the energy of sunlight. 10% of energy is present at each step and reaches the next level of consumers. So, if 100 J of energy is available to the lion, then the energy available to the producer is 10,000 J.

$$\underset{10,000\space\text{J}}{\text{Plants}}\xrightarrow{}\underset{1000\space\text{J}}{\text{Deer}}\xrightarrow{}\underset{100\space\text{J}}{\text{Lion}}$$

There are various types of wastes substances released into our environment. Those substances which are degraded into simpler form naturally by the action of microbes like bacteria or fungi are called biodegradable substances. Examples–Vegetables and fruit peels, paper, agricultural wastes etc.

Those substances which cannot be degraded into simpler forms naturally by the action of microbes are called non-biodegradable substances. Examples–Aluminium foils, plastic bottles, glass apparatus etc.

30. (i) Pole: It is the centre of the reflecting surface of the mirror.

(ii) Centre of curvature: It is the centre of the hollow sphere of which the reflecting surface of the mirror is a part.

(iii) Principal focus: Incident rays parallel to the principal axis, after reflection, either converge to or appear to diverge from a fixed point on the principal axis. This point is called the principal focus of a spherical mirror.

(iv) Principal axis: It is the straight line passing through the pole and centre of curvature of a spherical mirror.

(v) Radius of curvature: The radius of curvature of a spherical mirror is the radius of the hollow sphere of glass of which the mirror is a part.

(vi) Aperture: The portion of a mirror from which the reflection of light actually takes place is called the aperture of the mirror.

31. (i) The magnetic lines of force do not intersect one another due to the fact that the resultant force on a north pole at any point can be only in one direction. But, if the two magnetic lines of force intersect one another, then the resultant force on a north pole placed at the point of intersection will be along directions, which is not possible.

(ii) (a) The strength of magnetic field is directly proportional to the strength of current, so if the current in the conductor increases, the magnetic field around it also increases.

(b) On reversing the direction of the current, direction of the magnetic field will also be reversed.

(iii) Magnetic field lines between two magnets are shown below :

32. (i) When copper vessels are exposed to moist air, they form a green coating of basic copper carbonate [CuCO₃. Cu(OH)₂]. The sour substance such as lemon juice contain acid. Lemon juice contains citric acid. This acid dissolve the coating of copper oxides or basic copper carbonate present on the surface
of tarnished copper vessels and make them shining red-brown again.

$$\underset{\text{From moist air}}{2\text{Cu} + \text{CO}_{2} + \text{O}_{2} +\text{H}_{2}\text{O}}\xrightarrow{}\\\underset{\text{Basic copper carbonate (Green)}}{\text{CuCO}_3.\text{Cu(OH)}_2}$$

(ii) Copper does not react with cold water, hot water, or steam. However, iron reacts with steam. If the hot water tanks are made of steel (an alloy of iron), then iron would react vigorously with the steam formed from hot water to corrode the tank due to the formation of iron oxide.

$$\underset{\text{Iron}}{3\text{Fe}} + \underset{\text{Steam}}{4\text{H}_2\text{O}}\xrightarrow{}\\\underset{\text{Iron oxide}}{\text{Fe}_{3}\text{O}_{4}} +\underset{\text{Hydrogen}}{4\text{H}_{2}}$$

Therefore, copper is used to make hot water tanks and not steel.

(iii) Copper metal has high melting and boiling point, good conductor of electricity and can be drawn into thin wires. This is the reason behind the use of copper metal to make electrical wires.

33. (i) The process of transfer of pollen grains from the anther to the stigma of the same or different flower is known as pollination. The two types of pollination are self-pollination and cross-pollination.

(ii)

Section-D

Question No. 34 to 36 are long answer questions.

34. (i) Silver is covered with a thin layer of silver chloride, so it does not react with dilute hydrochloric acid.

$$\underset{\text{Silver}}{\text{Ag}} +\underset{\text{(dil.)\\Hydrochloric acid}}{\text{HCl}}\xrightarrow{}\text{No Reaction}$$

(ii) Bubbles of hydrogen gas are evolved when the lead is reacted with the acid.

$$\underset{\text{Lead}}{\text{Pb}} + \underset{\text{(dil.)Hydrochloric acid}}{\text{2HCl}}\xrightarrow{}\\\underset{\text{Lead}}{\text{PbCl}_{2}} +\underset{\text{Hydrogen}}{\text{H}_{2}}$$

(iii) The reaction of sodium is found to be highly explosive because sodium is a highly reactive metal. It reacts with hydrochloric acid explosively forming hydrogen gas along with the release of large amount of heat.

$$\underset{\text{Sodium}}{\text{2 Na(s)}} + \underset{\text{Hydrochloric acid}}{2\text{HCl}(aq)}\xrightarrow{}\\\underset{\text{Sodium chloride}}{\text{2 NaCl}(\text{aq})} + \underset{\text{Hydrogen}}{\text{H}_{2}g}\uparrow +\space \text{Heat}$$

(iv) The temperature of the reaction mixture rises when aluminium is added to the acid because the reaction is highly exothermic in nature.

$$\underset{\text{Aluminium}}{2\text{AI(s)}} + \underset{\text{Hydrogen chloride}}{6 \text{HCl(aq)}}\xrightarrow{}\\\underset{\text{Aluminium chloride}}{\text{2 AlCl}_{3}(\text{aq})} + \underset{\text{Hydrogen}}{3\text{H}_{2}(g)}$$

(i) CaOCl₂: Its chemical name is calcium oxychloride. It is also known as bleaching powder.

Preparation: Bleaching powder is produced by the action of chlorine on dry slaked lime.

$$\text{Ca(OH)}_{2} +\text{Cl}_{2}\xrightarrow{}\text{CaOCl}_2 {+ \text{H}}_2\text{O}$$

Uses: It is used as a bleaching agent in the textile industry.

$$\textbf{(ii)\space CaSO}_{\textbf{4}}.\frac{\textbf{1}}{\textbf{2}}\textbf{H}_{\textbf{2}}\textbf{O}\space\textbf{:}$$

It is calcium sulphate hemihydrate. It is also known as Plaster of Paris.

Plaster of Paris is prepared by heating

$$\frac{1}{2}\space\text{Gypsum at 373K.}$$

$$\text{CaSO}_{4}.2\text{H}_{2}\text{O}\xrightarrow{}\\\text{CaSO}_{4}.\frac{1}{2}\text{H}_{2}\text{O} +\frac{3}{2}\text{H}_{2}\text{O}$$

Uses: It is used to join bones, buildings and in dentistry.

(iii) NaHCO₃: Its chemical name is sodium hydrogen carbonate (NaHCO3). Also known as baking soda.

Preparation:

$$\text{NaCl + H}_2\text{O + CO}_2 + \text{NH}_3\xrightarrow{}\\\text{NH}_{4}\text{Cl} + \text{NaHCO}_{3}$$

Uses: It is used in the food industry and bakery, as an antacid and mild antiseptic.

35.

The heart is divided into the right and left side by the septum. The heart has four chambers, two relatively small upper chambers called atria or auricles and two larger lower chambers called ventricles. The walls of the ventricles are relatively thicker than atrial walls.
The two atria are separated from each other by a thin, muscular wall called the inter-atrial septum and the right and
left ventricles are by a thick-walled, inter-ventricular septum. The inter-atrial septum and inter-ventricular septum prevent mixing of deoxygenated blood in the right side of the heart with oxygenated blood in the left side of the heart.
The atria and ventricle on the same side are separated by a thick fibrous tissue called the atrioventricular septum.
The opening between the right atrium and the right ventricle is guarded by a valve called the tricuspid valve, whereas a
bicuspid valve guards the opening between the left atrium and the left ventricle.
The largest artery is the aorta which arises from the left ventricle and supplies blood to all the body parts except the lungs. Pulmonary artery that arises from the right ventricle carries deoxygenated
blood to lungs.
The openings of the right and left ventricles into the pulmonary artery and the aorta respectively are provided with the semilunar valves.
The valves allow the blood to flow only in one direction, i.e. from the atria to the ventricles and from the ventricles to the pulmonary artery or aorta.

The different methods of contraception are:

(1) Methods which create a mechanical barrier so that the sperm does not reach the egg. They include condoms on the penis or similar coverings on the vagina.

(2) A second category acts by changing the hormonal balance of the body so that eggs are not released and fertilisation does not occur. These are drugs taken as oral pills. However, as they change hormonal balance they cause side effects too.

(3) There are contraceptive devices placed in the uterus such as the loop or the Copper-T to prevent pregnancy. This could cause side effects like irritation in the uterus.

(4) Surgery is used to create blocks in the vas deferens of the male so that sperm transfer is prevented. Surgery is also used to block the fallopian tube so that the egg does not reach the uterus. While surgical methods are safe in the long run surgery itself could cause infections and other problems if not done properly.

36. The defect caused due to gradual weakening of ciliary muscles and diminishing flexibility of the eye lens is presbyopia. Presbyopia is the defect of the eye in which a person cannot see nearby objects comfortably and distinctly without corrective eye glasses. A presbyopic eye has a near point greater than 25 cm and is gradually increases as the eye becomes older. The type of lens required by such a person to improve the vision is bifocal lens.

A bifocal lens consists of both convex lens and concave lenses. The convex lens used in the bifocal lens to correct Hypermetropia (far-sightedness) and the concave lens is used to correct myopia (short sightedness).

(a) An arrangement for observing the scattering of light in the laboratory is as shown below.

(b)

On the screen, first orange red colour and then bright crimson red colour patch is observed.
From the other three sides of colloidal solution of sulphur in glass tank(T), blue colour is observed. This is because the very fine colloidal sulphur particles scatter away the blue colour from the path of beam and only red colour (least scattered) of the beam of white light reaches the screen through the solution.

Section-E

Question No. 37 to 39 are case - based/data -based questions with 2 to 3 short sub - parts. Internal choice is provided in one of these sub-parts.

37. (a) Environmental triggers such as light, or gravity will change the directions in which the plant parts grow in. These directional, or tropic, movements can be either towards the stimulus, or away from it. The shoots usually grow upwards and away from the Earth.

(b) The movement of plants in response to chemicals is called Chemotropism. One example of chemotropism is the growth of pollen tubes towards ovules.

The above activity shows the movement of plants in response to light.

38. (a) It is easier to obtain metal from its oxide, as compared to its sulphides and carbonates. Therefore, metal sulphides and carbonates must be converted into metal oxides prior to their reduction.

(b) Cinnabar (HgS) is an ore of mercury. When it is heated in air, it is first converted into mercuric oxide (HgO). Mercuric oxide is then reduced to mercury on further heating.

$$\text{2HgS(s)} + 3\text{O}_{2}(g)\xrightarrow{\text{heat}}\\\text{2HgO(s) + 2SO}_2\text{(g)}\\\text{2HgO(s)}\xrightarrow{\text{heat}}\text{2Hg(l) + O}_2\text{(g)}$$

(c) Highly reactive metals, such as sodium, calcium, aluminium, etc., are used as reducing agents because they can displace metals of lower reactivity from their compounds. For example, when manganese dioxide is heated with aluminium powder, the following reaction takes place.

3MnO₂(s) + 4Al(s) → 3Mn(l) + 2Al₂O₃(s) + Heat

The reaction of iron (III) oxide (Fe₂O₃) with aluminium is used to join railway tracks or cracked machine parts. This reaction is known as the Thermite reaction.

Fe₂O₃(s) + 2Al(s) → 2Fe(l) + Al₂O₃(s) + Heat

39. (i) The region surrounding a magnet, in which the force of the magnet can be detected, is said to have a magnetic field.

(ii) Inside the magnet, the direction of field lines is from its south pole to its north pole.

(iii) The relative strength of the magnetic field is shown by the degree of closeness of the field lines. The field is stronger, that is, the force acting on the pole of another magnet placed is greater where the field lines are crowded.

(iv) If the current is increased, the deflection also increases.